Field
The disclosed concept pertains generally to electric power distribution and metering and, more particularly, to electric power distribution systems that meter electric energy. The disclosed concept further pertains to methods of evaluating energy metering of an electric power distribution system.
Background Information
Meters are used by electric utilities to measure and bill for electricity usage. Typically, meters need to be accessible, replaceable, testable and tamper-resistant. Meters need to be accessible and readable by both the utility and its customers to ensure correct meter readings. Meters need to be replaceable in the event of a malfunction, and testable to verify accuracy. Also, a mechanism needs to be provided to protect against theft of power or, otherwise, improper or inadvertent bypassing or tampering of the meter, which results in inaccurate billing of actual electricity usage.
Conventional glass bulb meters meet these requirements and are accepted by public utility commissions due to their historical success in meeting the above four needs in a cost effective manner. The glass bulb meter is a relatively inexpensive, simple device used to accurately measure the energy (kWh) and peak demand power (kW) within an agreed upon demand window used at a customer premise. These meters were originally electromechanical devices, but are being replaced by electronic meters. These meters are accessible, although not necessarily private, since they are typically located on the outside of a building and are easily read by anyone who walks up to them. Such meters are easily removed and replaced by utility service personnel. Glass bulb meters can be bench tested using a known power source and they are also protectable by using lockout tags to prevent tampering.
Electric utilities are required by their public utility commissions to test the accuracy of their meters. These tests normally follow the ANSI C 12.1 and ANSI/ASQ Z1.9 standards. Typically, a statistical sampling plan is used to verify meter accuracy. This statistical sampling plan states that the sample will, 95 times out of 100, correctly determine whether at least 97.5% of a homogeneous lot of meters are within the range of accuracy specified by the utility.
ANSI C 12.1 allows other types of tests to verify metering accuracy including a periodic test schedule and a variable interval plan. These tests verify each individual meter used by the utility. This is clearly a better practice for the utility and its customers, however, meter deployments of most utilities are simply too large for this type of testing to be practical.
Automatic meter reading adds one-way communication, in order that a meter can communicate back to the electric utility office at regular intervals. This improves accessibility because now the data can be made accessible over the Internet or an appropriate, utility-owned communication network. Also, the electric utility no longer has to send “meter reader” personnel to physically read each meter, since the reading can be done automatically. The meter can also employ sensors, in order that if there is some kind of malfunction or if it detects tampering, then it can send a corresponding message to the electric utility.
Advanced meter infrastructure (AMI) or smart meter rollouts are currently employed in various service territories. AMI adds two-way communication between the meter and the electric utility. By adding the ability to “listen” in addition to being able to “talk”, electric utilities can realize additional benefits. Variable time of use schedules and real time pricing are two applications where the utility can change how the meter is billing the customer based on the conditions of the utility grid. Some smart meters have integrated service disconnects that can be triggered remotely if the utility bill is not timely paid. These meters may also include communication into the premise to communicate with end devices. This allows a utility to perform demand response or load control and actively manage participating loads on the utility grid. This new command functionality creates an additional metric to value a meter. While the benefits have not yet been fully realized and standard ways for end devices and the meter to communicate are still under development, smart grid demonstrations across the country are proving the value created by command functionality.
Electric vehicles (EVs) are a relatively new category of load on the utility grid and represent a huge potential growth of electricity demand from the grid. This is a double-edged sword for utilities—they want to sell more power, but want to do so during off-peak hours. A recent report shows that the current generation asset utilization in the U.S. is only about 47%. As a result, generation capacity does not need to be increased to support additional load, if power is consumed during off-peak times.
EVs have an additional benefit of reducing CO2 emissions. This improves air quality and reduces emissions. In places like California, this and the success of EVs is very important. However, California has a counter-intuitive, tiered approach to selling electricity. As a customer buys more energy, punitive action is taken against them, in order that the cost per kWh increases as usage increases. This creates a dilemma EVs put customers in a higher tier of electric prices, but help to reduce emissions and clean the air.
This situation has resulted in “utility grade sub-metering” in electric vehicle supply equipment (EVSE). California wants to subsidize the energy used to charge EVs, but currently takes punitive action against customers with electric vehicles. The solution is that the EV becomes a “special load” with a special rate structure, such that the consumer is encouraged to adopt the technology which is mutually beneficial to both the utility and the consumer. As EV and other “special loads” (e.g., on-site solar and wind generation; distributed energy storage; intelligent appliances) are added to a premise, it makes the utility's current methodologies for metering less effective and less beneficial to both the utility and the consumer. As a result, this presents an opportunity for the public utility commissions to accept alternative methodologies and form factors other than the current glass bulb meter. This would allow metering and billing of every load differently and separate from one another in a manner that does make it mutually beneficial.
There is room for improvement in electric power distribution systems.
There is also room for improvement in methods of evaluating energy metering of an electric power distribution system.